The design of radio frequency (RF) circuits requires careful attention to containment of the electrical and magnetic fields created at their operating frequencies. Instruments utilizing analog circuits at radio frequencies pose significant challenges in this area, as contrasted to digital circuit designs which require substantially less containment of radio frequencies due to the fact that digital circuits are far less sensitive to radiated interference. In analog circuits, isolation of one signal to another is vital to accurate circuit operation. Furthermore, escaping radiation can interfere with proper operation of nearby external electronics, such as radios, television receivers, and other devices.
Analog electronic instrumentation is typically encased within metal enclosures that are grounded to minimize radiation leakage to the exterior of the instrument and radiation cross coupling to other circuits. Openings in these enclosures require radiation gaskets, typically in the form of elongated metal spirals, braids, or flat spring forms that are compressed by pressure of a cover that bears against the gasket in only one direction. Such gaskets provide sealing to the cover along a single line extending across one cover surface. The dimensions and tolerances of the gaskets and covers are therefore critical to a good seal being established.
It is also well known that radio frequency interference (RFI) can occur within the various conductive elements of printed circuitboards as radio frequency signals are transmitted through selected traces. Guard traces are typically provided alongside such traces to minimize such interference. Signal traces in base circuitboards, used to interconnect modular RF signal circuits, are a potential source of radiation leakage in such instrumentation.
The present invention was designed to maximize the exterior shielding of analog electronic circuits by improvement of the enclosure and gasket technology used to prevent leakage of radiation from the interior operating environment of the circuits. It is directed specifically to the interconnection of such enclosures and a base circuitboard through which interconnections are made between modular circuits included within an electronic instrument. It relates the enclosures to the base circuitboard structure, so that the top ground plane of the base circuitboard completes the enclosures and contains the fields generated by the modular circuits. The present invention is also directed to the interconnections made between modular circuits included within an electronic instrument.